1. Field of the Invention
The invention relates to the field of digital data communication systems and a circuit arrangement and method for minimizing bit errors in such systems.
2. Description of the Related Art
In a digital receiver, digital data such as that transmitted via optical fibers or coaxial cables are converted back into digital data in the receiver by sampling the received signal. At a specific sampling time, a threshold decision is made as to whether a high or low voltage potential value is assigned to the received signal in a sampling interval.
For known receiver units, it is a standard practice that the sampling time at the height of the threshold for the threshold decision is determined and set upon initialization of the receiver unit. Due to changing system properties, however, the required values for an optimum sampling time and the optimum threshold change. Degeneration of values set once for initialization of the receiver unit are kept slight by a decision process when the changing system properties of the receiver unit are utilized in determining of the sampling time as well as of the threshold.
Given receiver units in ultra-high rate optical transmission systems in which it is not possible to adequately prescribe the system reserves in such a way, a monitoring path for setting the sampling time and/or the threshold is utilized in addition to a signal path. In a receiver unit in this type of transmission system, a first decision unit is integrated in the signal path and a second decision unit is integrated in the monitor path. The inputs of the first and second decision units are charged with the same received signals. The second decision unit in the monitor path serve, by a variation such as an artificial deterioration of the threshold and of the sampling time to respectively determine an optimum value for these without negatively influencing quality of the transmitted signal in the signal path. Whenever an improvement compared to the signal path has been identified, the first decision unit in the signal path takes the optimized values for the sampling time and the threshold.
In another method for controlling the threshold, given the precondition that the plurality of zeroes and ones of the transmitted digital signal sequence are in equally distributed, in a criterion for an optimized threshold control is derived by average formation in transmission paths that are highly affected by errors. This method, however, involves the disadvantage that it cannot be applied for optical transmission paths having a bit error rate on an order of magnitude of 10xe2x88x9210.
The invention is based on the object of specifying a circuit arrangement as well as a method for minimizing bit errors in the regeneration of a digital signal sequence.
This object is achieved by a circuit arrangement for minimizing bit errors in a regeneration of digital data signals comprising: 1) a decision unit that has a data signal input from which digital data signals enter the decision unit, a decision criterion input from which a decision criterion enters the decision unit, and a bit sequence output from which a bit sequence is output based on a sampling of the data input signal and of the decision criterion, 2) a correction unit having an input into which the bit sequence enters, an output from which the correction unit outputs a corrected bit sequence or an error signal after the unit corrects the bit sequence with an error correction, and 3) an error analysis unit having a first input into which the bit sequence or error signal is entered, a second input into which the corrected bit sequence is entered, and an output at which a decision criterion formed from the corrected bit sequence and the bit sequence or error signal is output, which employs the use of neighboring bits of the corrected bit sequence.
This object is also achieved by a method for minimizing bit errors in a regeneration of digital data signals comprising the steps of sampling the data signals and generating a bit sequence, correcting the bit sequence and generating a corrected bit sequence or an error signal, and forming decision unit criterion with which data signals are sampled from the corrected bit sequence or error signa and the bit sequence, and utilizing the neighboring bits of the corrected bit sequence.
The invention has the advantage that no additional optical reception components are required for regeneration of received, digital signal sequences.
The invention has the further advantage that no artificial deterioration of the bit error rate must be induced in order to find out the direction in which, for example, the sampling time must be varied.
Further characteristics are described below.